CHICAGO - WIND turbines, roof gardens and solar panels will join the pair of antennas atop the Sears Tower's staggered rooftops, said building officials who announced Wednesday that the skyscraper would undergo a US$350 million (S$510 million) green renovation.

The 5-year project would reduce the tower's electricity use by 80 per cent and save 24 million gallons of water a year, building owners and architects said.

Separately, a 50-story, 500-room privately funded luxury hotel with its own green components would be built next to the skyscraper in 3 1/2 to 5 years.

In March, London-based Willis Group Holdings announced that the Sears Tower would be renamed Willis Tower later this summer after the company moves 500 employees into the building. And construction is under way on the tower's Skydeck to add four enclosed glass-bottomed balconies.

The green project includes the installation of solar panels on the tower's 90th floor roof to heat water used in the building.

Different types of wind turbines will be positioned on the tower's tiered roofs and tested for efficiency. And between 2,787 sq metres and 35,000 square feet 3,250 sq metres of roof gardens will be planted.

Other changes to the 110-story skyscraper, the tallest building in the United States, include improvements to the 16,000 window pieces along the outside of the tower to save heating energy; mechanical system upgrades; updates to the building's 104 elevators; an advanced lighting control system and restroom renovations aimed at saving water.

Officials dispelled rumours the building's black exterior would be painted silver to increase energy efficiency.

The project should create 3,600 jobs, officials said, and will include a learning centre on the ground floor showcasing green efforts to the public.

Officials say they'd like the tower to achieve 'LEED' status, otherwise known as Leadership in Energy and Environmental Design, a standard monitored by the US Green Building Council. -- AP